Process for the electrochemical production of 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid

ABSTRACT

A process for the electrochemical production of 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage of a mixture of cis- and trans-3,3,5-trimethylcyclohexanol.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a utility application based on, and claimingbenefit to, German Application No. 102014202502.8, filed on Feb. 12,2014.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF THE MATERIAL ON THE COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates the electrochemical production of2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid byelectrochemical oxidative ring cleavage of a mixture of cis- andtrans-3,3,5-trimethylcyclohexanol.

2. Description of the Related Art Including Information Disclosed Under37 CFR 1.97 and 1.98

According to the current state of the art, the production of2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid (TMAS) from amixture of cis- and trans-3,3,5-trimethylcyclohexanol (TMCol) iseffected by oxidative ring cleavage using nitric acid.

Disadvantages of this process due to the use of nitric acid are, interalia, corrosion, safety issues, and the formation of nitrous components.

It is mentioned in Hans-Jürgen Schäfer, Oxidation of organic compoundsat the nickel hydroxide electrode, Topics in Current Chemistry, Vol.142, pp. 101-129, 1987, Johannes Kaulen, Hans-Jürgen Schäfer, Oxidationof alcohols by electrochemically regenerated nickel oxide hydroxide.Selective oxidation of hydroxysteroids, Tetrahedron Vol. 38 No. 22 pp.3299-3308, 1982, and Johannes Kaulen: Oxidation of diols and secondaryalcohols at the nickel hydroxide electrode. Use for selective oxidationof hydroxysteroids [in German], dissertation at the University ofMünster 1981, that the electrochemical oxidation of cyclohexanol atrelatively high temperatures proceeds, to some extent, with adipic acidbeing formed by ring cleavage. The reaction is effected using nickelhydroxide electrodes. Yields of adipic acid of 16% and 24% at 25° C. andof 42% at 80° C. were obtained.

B. V. Lyalin, V. A. Petrosyan, Electrosynthesis of adipic acid byundivided cell electrolysis, Russian Chemical Bulletin, InternationalEdition, Vol. 53 No. 3 pp. 688-692, March, 2004, likewise addresseselectrochemical oxidative ring cleavage of cyclohexanol to give adipicacid at nickel hydroxide electrodes. This paper reports a maximum yieldof adipic acid of 46.7% at a simultaneous current yield of 11.5%.By-products in the reaction are succinic acid and glutaric acid formedin a yield of 6.3% and 11.5%, respectively. These components are formedby oxidative elimination of CH₂ groups from the C6 core structure ofcyclohexanol.

Adipic acid is formed as the disodium salt in the above publications.The salt can be converted into the H acid form by simple acidificationwith hydrochloric acid, for example.

The solubility of cyclohexanol in water is 40 g/l at 20° C. Thesolubility of the trimethylated cyclohexanol, TMCol, in water is only1.8 g/l at 20° C.

BRIEF SUMMARY OF THE INVENTION

It was found that, surprisingly, TMCol may be converted into2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid (TMAS) byelectrochemical oxidative ring cleavage under alkaline conditionsdespite the low solubility in water. The conversion proceeds via theintermediate 3,3,5-trimethylcyclohexanone (TMCon).

Advantages of this process compared to the process mentioned above dueto the use of nitric acid being avoided are: avoidance of corrosivity,no formation of nitrous gases.

These and other objects are achieved by the present invention, whichelectrochemically produces 2,2,4-trimethyladipic acid and2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage ofa mixture of cis- and trans-3,3,5-trimethylcyclohexanol in an aqueousalkaline solution.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1: Electrolysis batch apparatus for conversion of TMCol into TMAS.

FIG. 2: Electrolysis batch apparatus for conversion of TMCol into TMAS.

FIG. 3 a: A cross-section of a Swiss-roll continuous flow electrolyticcell.

FIG. 3 b: Section through sandwich construction of a Swiss-rollcontinuous flow electrolytic cell.

FIG. 3 c: Rolled-up sandwich construction of a Swiss-roll continuousflow electrolytic cell.

FIG. 4 a: An empty electrolytic cell.

FIG. 4 b: An electrolytic cell filled with nickel pellets.

DETAILED DESCRIPTION OF THE INVENTION

In this specification, the words “a” and “an” and the like carry themeaning of “one or more.” The phrases “selected from the groupconsisting of,” “chosen from,” and the like include mixtures of thespecified materials. Terms such as “contain(s)” and the like are openterms meaning ‘including at least’ unless otherwise specifically noted.Where a numerical limit or range is stated, the endpoints are included.Also, all values and subranges within a numerical limit or range arespecifically included as if explicitly written out.

The invention provides a process for the electrochemical production of2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid byelectrochemical oxidative ring cleavage of a mixture of cis- andtrans-3,3,5-trimethylcyclohexanol in aqueous alkaline solution.

The electrochemical conversion of TMCol into TMAS is effected in anelectrolytic cell. The process is in principle not limited to aparticular type of electrolytic cell.

The reaction is performed in aqueous alkaline solution. Useful alkalisinclude in principle all known inorganic bases. Alkali metal hydroxides,such as LiOH, NaOH, KOH, and soluble alkaline earth metal hydroxides arepreferred. In accordance with the invention, it is particularlypreferable to use aqueous sodium hydroxide solution or aqueous potassiumhydroxide solution.

Materials useful in principle as anode material include transitionmetals. It is preferable to use nickel.

Materials useful in principle as cathode material include transitionmetals. It is preferable to use stainless steel.

Preference for use as the anode is given to electrode types having alarge specific surface area. Gauzes, pellet beds, and foams areparticularly preferred.

The electrolysis may be effected batchwise or continuously.

The electrolysis may be carried out in a batch electrolytic cell andalso in a continuous flow electrolytic cell. It is preferable to carryout the electrolysis in a continuous flow electrolytic cell.

The electrolysis is preferably run at an elevated temperature. Atemperature of from 60° C. to 100° C. is preferred. A temperature offrom 70° C. to 90° C. is particularly preferred.

Preferred variants of the process are described hereinbelow.

Variant 1

The electrochemical conversion of TMCol into TMAS may be effected in theelectrolysis batch apparatus shown in FIG. 1. The cathode is a stainlesssteel plunger and the anode is a cylindrical nickel gauze. The solutionintroduced into the apparatus is stirred by a magnetic stirrer bar andheated using a thermostat. A pump facilitates additional externalcirculation of the solution in order to further enhance commixing.

Variant 2

The electrochemical conversion of TMCol into TMAS may alternatively beeffected in the electrolysis apparatus shown in FIG. 2. Said apparatuscomprises an electrolytic cell, a temperature-controllable receiver, apump, and a cooler.

The electrolytic cell is a continuous flow electrolytic cell with astainless steel cathode and a nickel anode.

Various pump types may be used as pumps for the electrolysis apparatusshown in FIG. 2. Pumps which in addition to the conveying effect achievedispersion of the organic substrate in the alkaline aqueous solution areparticularly suitable, for example peripheral pumps.

Variant 3

The continuous flow electrolytic cell employed may specifically be aSwiss-roll cell (see “Peter. M. Robertson, F. Schwager, A new cell forelectrochemical processes, Journal of Electroanalytical Chemistry Vol.65 pp. 883-900, 1975”, “Peter Seiler, Peter M. Robertson, The anodicoxidation of diacetone-L-sorbose on an industrial scale [in German],Chimia Vol. 36 No. 7/8 pp. 305-312, 1982”). The Swiss-roll cell is shownin FIG. 3. This electrolytic cell type comprises a nickel gauze and astainless steel gauze, one above the other, separated by a polypropylenefabric and wound around a central nickel rod. Here, the nickel rodcontacts only the nickel gauze. The cell housing consists of stainlesssteel which contacts only the stainless steel gauze.

Variant 4a

It was found that it is likewise possible to use an electrolytic cellmade of a stainless steel housing, a central nickel rod and nickelpellets introduced into the cell. The cell type is shown in FIG. 4.Here, the nickel pellets are in electrical contact with the centralnickel rod.

The nickel pellets are electrically insulated from the stainless steelhousing by a polypropylene fabric disposed on the inside of thestainless steel housing.

Variant 4b

It was further found that the cell type shown in FIG. 4 may be furnishedwith a flat-ply nickel foam and a stainless steel gauze instead of withnickel pellets. Said foam and gauze are wound around the central nickelrod, one above the other, with a polypropylene fabric separating them.Here, the nickel rod contacts only the nickel foam. The cell housingconsists of stainless steel which contacts only the stainless steelgauze.

Prior to TMAS electrosynthesis, the nickel anode surface may beconditioned in order to electrochemically deposit a thin multilayerednickel oxide hydroxide top layer onto the nickel anode surface.

This may, for example, be carried out as follows:

280 ml of a conditioning solution comprising 0.1 mol/l of NiSO₄×6H₂O,0.1 mol/l of NaOAc×3H₂O, and 0.005 mol/l of NaOH in distilled water wasintroduced into the electrolysis. In the case of the electrolysisapparatus of FIG. 2, the conditioning solution was additionallyrecirculated. The nickel gauze was alternately polarised as the anode orthe cathode for a short time (10 s) by automatic electrode polarisationswitching until a black surface layer was formed (current 150 mA, charge100 C). The conditioning solution was subsequently discharged from theentire apparatus. The entire apparatus was then thoroughly rinsed withdistilled water. The freshly activated electrolytic cell was thenimmediately used for electrolysis.

To carry out electrosynthesis of TMAS, the electrolytic cell was filledwith water and also sodium hydroxide and TMCol dissolved therein. Therecirculated solution was then brought to the desired temperature. Theelectrolysis was carried out by passing electrical current through thecell galvanostatically for several hours.

Upon completion of the electrolysis, the solution was completelydischarged from the electrolysis apparatus and the electrolysisapparatus was then rinsed out with DM water. The electrolysis apparatuswas left dry between experiments. The combined solution from theelectrolysis apparatus was worked up in order to isolate TMCol, TMCon,TMAS, and any by-products upon completion of the electrolysis.

EXAMPLES Example 1

The electrolysis was carried out as described above in the electrolysisbatch apparatus shown in FIG. 1 using a wound 100 mesh nickel gauze of0.1 mm nickel wire having an area of 10 cm*25 cm and an interiorlydisposed round stainless steel plunger of 7 cm in diameter.

260 ml of water, 11.2 g of sodium hydroxide, and 5.73 g of TMCol werecharged to the electrolytic cell.

The electrolysis was carried out by passing 2 A through the cell for 6hours. The temperature was 80° C.

2.45 g of TMCol, 2.34 g of TMCon, and 1.06 g of TMAS were isolatedfollowing work-up. The yield of TMAS based on the TMCol employed was14%.

Example 2

The electrolysis was carried out as described above in the electrolysisapparatus shown in FIG. 2 using a Swiss-roll electrolytic cell shown inFIG. 3 comprising a wound 100 mesh nickel gauze of 0.1 mm nickel wirehaving an area of 6.5 cm*24.5 cm, a polypropylene fabric, and a wound100 mesh stainless steel gauze of 0.114 mm stainless steel wire havingan area of 6.5 cm*26.5 cm.

260 ml of water, 11.2 g of sodium hydroxide, and 5.93 g of TMCol werecharged to the electrolysis apparatus. A peripheral pump was used.

The electrolysis was carried out by passing 2 A through the cell for 24hours. The temperature was 80° C.

0.05 g of TMCol, 0.03 g of TMCon, and 2.70 g of TMAS were isolatedfollowing work-up. The yield of TMAS based on the TMCol employed was34%.

Example 3

The electrolysis was carried out as described above in the electrolysisapparatus shown in FIG. 2 using an electrolytic cell shown in FIGS. 4 aand 4 b comprising nickel pellets (bed volume 60 cm³).

264 ml of water, 11.2 g of sodium hydroxide, and 5.93 g of TMCol werecharged to the electrolytic cell. A peripheral pump was used.

The electrolysis was carried out by passing 2 A through the cell for 24hours. The temperature was 80° C.

0.06 g of TMCol, 0.04 g of TMCon, and 2.52 g of TMAS were isolatedfollowing work-up. The yield of TMAS based on the TMCol employed was32%.

Example 4

The electrolysis was carried out as described above in the electrolysisapparatus shown in FIG. 2 using an electrolytic cell shown in FIG. 3 acomprising a wound flat-ply nickel foam having an area of 6.5 cm*19 cm,a polypropylene fabric, and a wound 100 mesh stainless steel gauze of0.114 mm stainless steel wire.

264 ml of water, 11.2 g of sodium hydroxide, and 5.93 g of TMCol werecharged to the electrolytic cell. A peripheral pump was used.

The electrolysis was carried out by passing 2 A through the cell for 17hours. The temperature was 80° C.

0.09 g of TMCol, 0.14 g of TMCon, and 2.06 g of TMAS were isolatedfollowing work-up. The yield of TMAS based on the TMCol employed was26%.

Example Work-Up

The purpose of the work-up of the electrolysis solution describedhereinbelow was to isolate TMCol, TMCon, TMAS, and any by-products uponcompletion of the electrolysis and to subsequently determine conversion,yield, and selectivity.

50 g of sodium chloride were added to the aqueous solution poured out ofthe electrolysis apparatus.

The alkali aqueous phase was extracted with methyl tert-butyl ether(analytical grade) to remove remaining TMCol and TMCon by repeated (atleast 4-fold) extraction in a separating funnel.

The ether phase was dried with anhydrous magnesium sulphate. To thisend, magnesium sulphate was added to the ether phase until newly addedmagnesium sulphate remained in the liquid in the form of fine grains inthat clumping no longer occurred. The magnesium sulphate wassubsequently filtered off.

The ether was removed by rotary evaporation. The rotary evaporator wasinitially operated at atmospheric pressure. The boiling point of thesolution increased significantly towards the end of the distillativeremoval. Accordingly, a slight vacuum was applied and the underpressurewas increased as the concentration of MTBE in the solution was reducedin order always to achieve a sufficient distillation rate (up to 300mbar at 90° C.). The distillation at 300 mbar and 90° C. was continueduntil the head temperature in the rotary evaporator fell to and remainedconstant at room temperature.

Unreacted TMCol and TMCon were left behind in a residual amount of MTBE.These compounds were analysed by gas chromatography to determine purityand quantity.

TMAS was isolated by perforation. A relatively large liquid volume wasrequired for the perforator. The mixture was diluted with wateraccordingly.

The alkaline aqueous phase was subsequently acidified with concentratedhydrochloric acid to a pH of 1.

The acidified aqueous phase was perforated with MTBE (analytical grade)for 48 h.

The ether phase was subsequently dried with anhydrous magnesiumsulphate. To this end, magnesium sulphate was added to the ether phaseuntil newly added magnesium sulphate remained in the liquid in the formof fine grains in that clumping no longer occurred. The magnesiumsulphate was subsequently filtered off.

The MTBE was removed by rotary evaporation. The rotary evaporator wasinitially operated at atmospheric pressure. The boiling point of thesolution increased significantly towards the end of the distillativeremoval. Accordingly, a slight vacuum was applied and the underpressurewas increased as the concentration of MTBE in the solution was reducedin order always to achieve a sufficient distillation rate (up to 300mbar at 90° C. but not sufficient for quantitative removal of MTBE). Thedistillation at 300 mbar and 90° C. was continued until the headtemperature in the rotary evaporator fell to and remained constant atroom temperature.

TMAS and by-products were left behind in a residual amount of MTBE afterthe distillative removal and were quantitatively determined by gaschromatography following etherification with diazomethane.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein. In thisregard, certain embodiments within the invention may not show everybenefit of the invention, considered broadly.

1. A process, comprising: electrochemically producing 2,2,4-trimethyladipic acid and 2,4,4-trimethyladipic acid by electrochemical oxidative ring cleavage of a mixture comprising cis- and trans-3,3,5-trimethylcyclohexanol in an aqueous alkaline solution.
 2. The process of claim 1, wherein the aqueous alkaline solution is an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution.
 3. The process of claim 1, wherein the electrochemical oxidative ring cleavage is performed by electrolysis in an electrolytic cell comprising a cathode and an anode, wherein the electrolytic cell is a batch electrolytic cell or a continuous flow electrolytic cell.
 4. The process of claim 3, wherein the electrolysis is carried out in a continuous flow electrolytic cell.
 5. The process of claim 3, wherein the anode is a nickel anode.
 6. The process of claim 3, wherein the cathode is a stainless steel anode.
 7. The process of claim 3, wherein the anode is in the form of a gauze, a pellet bed, or a foam.
 8. The process of claim 3, wherein anode is a nickel gauze, a nickel pellet bed, or a nickel foam.
 9. The process of claim 5, further comprising: electrochemically depositing a thin multilayered nickel oxide hydroxide top layer onto a surface of the nickel anode.
 10. The process of claim 3, wherein the electrolysis is run at elevated temperature.
 11. The process of claim 3, wherein the electrolysis is carried out at temperature from 60° C. to 100° C.
 12. The process of claim 3, wherein the electrolysis is carried out at temperature from 70° C. to 90° C. 